He did threaten to assassinate President Trump though. I guess he didn't act on it.

It was a clear sign of TDS, but I don't think he intended it as an actual threat so much as a joke, sort of like the "...in Minecraft" jokes you see around here at times.

In 2017, he was introducing a drive-in screening of "The Libertine" and the following exchange occurred:

Depp: "Can you bring Trump here?"

Crowd: Boos and jeers.

Depp: "No, no, no, you misunderstand completely. I think he needs... help. When was the last time an actor assassinated a president? I want to clarify: I’m not an actor. I lie for a living. However, it’s been awhile, and maybe it’s time."

Unlike Kathy Griffin, he seems to have had more self-awareness about it from the beginning, as he directly followed this John Wilkes Booth/Trump assassination joke up with:

"By the way, this is going to be in the press and it’ll be horrible. It’s just a question; I’m not insinuating anything."

The secret service paid him a visit to make sure that he was just joking.

He fully apologized for it the next day, and unlike Kathy Griffin, never retracted his apology or played victim over the backlash. Here's his apology:

"I apologize for the bad joke I attempted last night in poor taste about President Trump. It did not come out as intended, and I intended no malice. I was only trying to amuse, not to harm anyone."